I presume you’re talking about a feature like this: https://tagboard.com/product/guides-and-remote-refresh-capab...

In page layout software, the thin UI elements bordering the left side and top side of the page, with the little tick marks, is called a ruler. The tick marks on the ruler are called rules (just like the rules on a physical ruler used for measuring things). When you click/drag on the ruler elements, you create guides (or guidelines).

I’ve never seen “ruler guides” verbatim, but I would take that to be shorthand for “guides one could create using the ruler” (which would be a mouthful) to disambiguate the word “guide” when there isn’t sufficient context for the reader to likely understand what was meant.

The guides themselves are not rulers.